The application of cost effectiveness analysis to derive a formulary for urinary tract infections.

According to economic principles an inappropriate prescription is the choice of an antimicrobial with higher/equivalent cost and lower effectiveness (or higher cost and equivalent/lower efficacy) than an alternative (in this case, the former is specified as a "dominated" drug). To identify cost-effective antibiotics we applied the principles of incremental cost-effectiveness analysis (ICEA) to microbiological data of San Bortolo Hospital. Its 27 wards were grouped in 9 functional areas. The resistance patterns of 8 urinary pathogens in the 1997 microbiology data base were assessed. The measure of antibiotic effectiveness was expressed as the percentage of isolates susceptible to each antibiotic tested. The difference in cost (i.e. the incremental change) between each antibiotic and the next more expensive alternative was calculated, and compared with the incremental change in effectiveness. Calculations were made for each pathogen. The antibiotics remaining after exclusion of all "dominated" antibiotics were pooled on a list defined as "Specific Area Formulary". The implications of the use of economic principles within a general antimicrobial policy are discussed.